The present invention relates to an antenna device and portable equipment, and more particularly, to an antenna device and portable equipment capable of reducing a size and weight thereof.
In recent years, a portable telephone has been widely spread. In mobile communication to use this portable telephone or the like, transmission waves are subjected to multi-reflection or scattering caused by buildings or the like present between a portable telephone as a mobile station and a base station. For this reason, polarization fluctuation of radio waves and others occur, resulting in level fluctuation of a received signal in a portable telephone and in turn, in deterioration in communication quality. In order to alleviate such deterioration in communication quality, there has been employed the diversity reception in which radio waves are received using two antennae and received signals through the antennae are synthesized or one thereof at a higher level is selected, thereby alleviating an influence of level fluctuation on a received signal.
FIG. 14 is a view showing a conventional portable telephone in a simplified manner. Description will be given of the conventional portable telephone with reference to FIG. 14.
Referring to FIG. 14, a portable telephone 101 adopts a so-called space diversity reception scheme as a measure to alleviate the deterioration in communication quality, including: two antennae of a whip antenna 150; and a built-in antenna 151 such as a flat plate antenna mounted inside a case of portable telephone 101.
In portable telephone 101 shown in FIG. 14, since antenna 150 and built-in antenna 151 for transmitting/receiving radio waves in the same band are installed adjacent to each other, a problem has been arisen that antenna 150 and built-in antenna 151 are electromagnetically coupled with each other to deteriorate an efficiency of the antenna.
Furthermore, as another type of the diversity reception, there has also been known a so-called polarization diversity reception scheme using a patch antenna. FIGS. 15 and 16 are model diagrams each showing an antenna device adopting a polarization diversity reception scheme.
Referring to FIG. 15, a patch antenna 152 is mounted on a board 103. Feed points 105a and 105b connected to a feed source are provided on adjacent sides of the periphery of patch antenna 152. By switching between feed points 105a and 105b, a plane of polarization of the patch antenna can be changed over from one of two directions indicated by two arrow marks 153 and 154 to the other. Moreover, as shown in FIG. 16, in the patch antenna 152, by switching between ground points 114a and 114b instead of feed points, switching between planes of polarization can also be realized. Referring to FIG. 16, ground points 114a and 114b grounding patch antenna 152 to the board are provided on adjacent side of a periphery of patch antenna 152. Furthermore, a feed point 105 connected to a feed source is provided on patch antenna 152.
Since such a patch antenna has a large antenna size, however, it, as was in the prior art, has been hard to be applied to portable equipment such as a portable telephone requiring reduction in size and weight.
As described above, in portable equipment such as a portable telephone requiring reduction in size and weight, it has been hard to suppress deterioration in communication quality without reducing an efficiency of an antenna.
The present invention has been made in order to solve such a problem and it is an object of the present invention to provide an antenna device and portable equipment capable of reducing a size and weight thereof and preventing deterioration in communication quality to be otherwise caused by polarization fluctuation of a radio wave and others without decreasing an antenna efficiency.
An antenna device in a first aspect of the present invention includes: a conductive board having one end portion and the other end portion opposite the one end portion; a flat plate antenna; first current direction change means; and second current direction change means. The flat plate antenna is mounted on the board with a dielectric interposing therebetween and when feeding a current thereto to excite, a current also flows in the board. The first current direction change means changes a direction of the current flowing in the board to a first direction when exciting said antenna and located on the one end portion of the board. The second current direction change means changes a direction of the current flowing in the board to a second direction different from the first direction when exciting the antenna and located on the other end portion of the board.
With such a construction adopted, directions of a strength of a radio wave radiated from the antenna device including the antenna and the board can be changed therebetween in respective cases where a direction of a current flowing in the board is the first direction and where a direction of a current flowing in the board is the second direction. That is, the directivity of the antenna can be changed. Here, the first direction is, for example, a direction along a diagonal line extending from the one end portion of the board to the opposite corner of the board and the second direction is exemplified as a direction along a diagonal line extending from the other end portion of the board to the opposite corner of the board. Furthermore, since a direction of the current flowing in the board is different according to the first direction or the second direction, a main polarization direction of the antenna device in each of the respective cases is different from that in the other cases. That is, by changing a direction of current flowing in the board from the first direction to the second direction and vice versa, directivity and a polarization direction of the antenna device can be changed. Therefore, an antenna device can be realized that operates as if it had two antennae different in directivity and polarization from each other using one antenna. As a result, the diversity reception can be implemented using one antenna. Accordingly, since no necessity arises for two antennas, which was required in a conventional practice, thereby preventing from occurrence of a problem of electromagnetic coupling between two antennas.
Furthermore, since functions of two antennas are realized with one antenna, a size and weight of an antenna device can be reduced compared with those in a case where two separate antennas are installed.
In the antenna device according to the above first aspect, the antenna may be installed so as to extend from a position on the one end portion of the board to a position on the other end portion of the board. The first current direction change means may include first feed means, which is connected to one portion of the antenna located on the one end portion of the board, for exciting the antenna and first feed control means for controlling feed of a current to the antenna from the first feed means. The second current direction change means may include second feed means, which is connected to another portion of the antenna located on the other end portion of the board, for exciting the antenna and second feed control means for controlling feed of a current to the antenna from the second feed means.
In this case, by switching between the first and second feed means using the first and second feed control means, a position of a feed point of the antenna can be changed over from a position in the one portion of the antenna to a position in the second portion of the antenna. By switching between positions of feed points in this way, a direction of the current flowing in the board can be easily changed over from the first direction to the second direction and vice versa. As a result, since an antenna device can be realized that operates as if it had two antennas different in directivity and polarization from each other using one antenna, the diversity reception can be realized using one antenna.
The antenna device according to the above first aspect may further include feed means for exciting the antenna. The antenna may be installed so as to extend from a position on the one end portion of the board to a position on the other end opposite the one end portion of the board. The first current direction change means may include a first ground means electrically connecting one portion of the antenna located on the one end portion of the board with the one end portion of the board and a first ground control means controlling connection of the first ground means with the antenna. The second current direction change means may include a second ground means electrically connecting a second portion of the antenna located on the other end portion of the board with the other end portion of the board and a second ground control means controlling connection of the second ground means with the antenna.
In this case, by switching between the first and second ground means, a position of a ground point of the antenna can be changed over from a position in the one portion of the antenna to a position in the second portion of the antenna. By switching between positions of the ground points in this way, a direction of the current flowing in the board can be easily changed over from the first direction to the second direction and vice versa. As a result, since an antenna device can be realized that operates as if it had two antennas different in directivity and polarization from each other using one antenna, the diversity reception can be realized using one antenna.
In the antenna device according to the above first aspect, the feed means is preferably connected to the central portion of the antenna; in the first ground means, the one end portion of the board is preferably connected to the one portion of the antenna at a first ground point of the one portion of the antenna; and in the second ground means, the other end portion of the board is preferably connected to the second portion of the antenna at a second ground point of the second portion of the antenna. The first ground point and the second ground point are preferably located at positions in bilateral symmetry with respect to the central portion of the antenna.
In this case, since the first and the second ground points are preferably located positions in bilateral symmetry with respect to the central portion of the antenna, common feed means for the first and second ground points can be provided at the central portion of the antenna. As a result, a construction of the antenna device can be simplified as compared with that in a case where two feed means corresponding to the first and second ground points are provided in an antenna device.
In the antenna device according to the above first aspect, the antenna may be installed so as to extend from a position on the one end portion of the board to a position on the other end portion opposite the one end portion of the board, and the first current direction change means may include: a first ground means electrically connecting one portion of the antenna located on the one end portion of the board to the one end portion of the board; a first feed means, connected to the one portion of the antenna located on the one end portion of the board, and for exciting the antenna; and a first feed ground control means switching between the first ground means and the first feed means. The second current direction change means may include: a second ground means electrically connecting a second portion of the antenna located on the other end portion of the board to the other end portion of the board; a second feed means, connected to the second portion of the antenna located on the other end portion of the board, and for exciting the antenna; and a second feed ground control means switching between the second ground means and the second feed means.
In this case, by controlling the first and second feed ground control means, a feed point and a ground point of the antenna can be arbitrarily provided in one of a region located on the one end portion of the board and a region located on the other end portion of the board. By switching between positions of a ground point and a feed point in this way, a direction of the current flowing in the board can be easily changed over from the first direction to the second direction and vice versa. As a result, since an antenna device can be realized that operates as if it had two antennas different in directivity and polarization from each other using one antenna, the diversity reception can be realized using one antenna.
In the antenna device according to the above first aspect, an electrical length of the antenna is preferably substantially xc2xc times a wavelength of a radio wave that can be received by the antenna.
In this case, a so-called xcex/4-wave antenna (xcex indicates a wavelength of a radio wave) is advantageous in reducing its size and by using such an antenna, further reduction in size and weight of an antenna device can be realized.
In the antenna device according to the above first aspect, the antenna preferably includes a first element capable of receiving a radio wave having a first frequency; and a second element capable of receiving a radio wave having a second frequency different from the first frequency.
In this case, by applying the present invention in a multi-frequency antenna device including the first and second elements, a direction of a current flowing in the board can be changed over from the first direction to the second direction and vice versa. Thereby, directivity and a polarization direction of an antenna device can be changed. That is, since one multi-frequency antenna can operates as if it were two antennas different in directivity and polarization from each other, the diversity reception can be easily realized using one multi-frequency antenna.
In the antenna device according to the above first aspect, the first current direction change means may include: a first feed source feeding a current having a first frequency for exciting the antenna; a second feed source feeding a current having a second frequency different from the first frequency for exciting the antenna; a first filter transmitting a current having the first frequency; and a second filter transmitting a current having the second frequency. The first feed source may be connected to a first common connection point of the antenna through the first filter, and the second feed source may be connected to the first common connection point of the antenna through the second filter. The second current direction change means may include: a third feed source feeding a current having the first frequency for exciting the antenna; a fourth feed source feeding a current having the second frequency different from the first frequency for exciting the antenna; a third filter transmitting a current having the first frequency; and a fourth filter transmitting a current having the second frequency. The third feed source may be connected to a second common connection point of the antenna through the third filter, and the fourth feed source may be connected to the second common connection point of the antenna through the fourth filter.
In this case, with the first and second filters used, the first and second feed source feeding currents having respective different frequencies can be connected to the first common connection point of the antenna. Furthermore, with the third and fourth filters used, the third and fourth feed source feeding currents having respective different frequencies can be connected to the second common connection point of the antenna. That is, since plural feed sources can be connected to the antenna by one connection point, the number of connection points of feed sources to the antenna can be reduced. As a result, a construction of the antenna can be simplified. Hence, the antenna device can be reduced in size and weight.
In the antenna device according to the above first aspect, the antenna may include a part having a function as a conductive wire for a current fed to the antenna and a function as a matching element.
In this case, since no necessity arises for installment of a separate matching element in addition to the antenna, a simpler construction of the antenna device can be realized. Hence, the antenna device can be reduced in size and weight.
In the antenna device according to the above first aspect, the first current direction change means may includes: a first matching circuit member; and a first feed means electrically connected to the antenna through the first matching circuit member, and the second current direction change means may include: a second matching circuit member; and second feed means electrically connected to the antenna through the second matching circuit member.
In this case, with the first and second matching circuits used, a characteristic of the antenna can be finely adjusted.
Portable equipment in another aspect is provided with the antenna device according to the first aspect.
With such construction adopted, since one antenna device can operate as if it were two antennas different in directivity and polarization from each other, reduction in size and weight of portable equipment can be achieved compared with an antennas device in a case where two antennas are actually installed.